FIG. 1 is a diagram showing a configuration of a conventional board connection on a transmission line disclosed in Japanese patent application laid-open No. 4-28182/1992, for example. In FIG. 1, the reference numeral 1 designates a daughter card; 2 designates a transmission path of the daughter card 1; 3 designates a signal through hole (through hole used for a signal) of the daughter card 1; 4 designates a ground layer; 5 designates a ground through hole (through hole used for a ground) of the daughter card 1; 6 designates a backplane; 7 designates a transmission path of the backplane 6; 8 designates a signal through hole of the backplane 6; 9 designates a ground layer; 10 designates a ground through hole of the backplane 6; 11 designates a connector having its connector pin 11a inserted into the signal through hole 3 of the daughter card 1 and its connector pin 11b inserted into the signal through hole 8 of the backplane 6; and 12 designates a connector having its connector pin 12a inserted into the ground through hole 5 of the daughter card 1, and its connector pin 12b inserted into the ground through hole 10 of the backplane 6.
Next, the operation will be described.
The connector pin 11a of the connector 11 is inserted into the signal through hole 3 of the daughter card 1, and the connector pin 11b of the connector 11 is inserted into the through hole 8 of the backplane 6.
Thus, the transmission path 2 of the daughter card 1 is electrically connected to the transmission path 7 of the backplane 6.
Accordingly, a signal output from a driver or the like installed in the daughter card 1 is transmitted from the transmission path 2 of the daughter card 1 to the transmission path 7 of the backplane 6 via the connector 11.
However, if the characteristic impedance of the transmission path 2 of the daughter card 1 differs from that of the transmission path 7 of the backplane 6, the impedance mismatching will bring about signal reflection, which prevents high-speed transmission of the signal.
In view of this, to minimize the signal reflection due to the impedance mismatching, the conventional transmission lines make a contrivance as to the placement of the ground and reducing the length of the fitting portion of the connector 11.
With the foregoing arrangement, the conventional communication equipment can control the signal reflection as long as the transmission speed of the signal is within a certain limit. However, as the transmission speed of the signal further increases, a problem arises of being unable to control signal reflection sufficiently by only contriving the placement of the ground and the length of the fitting portion of the connector 11.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide a stub line for controlling the signal reflection even if the transmission speed of the signal is increased.